Barrika,
Did you take the ladder off the rear sight, by pulling the drift-pin?? The leaf spring is fairly stout, and when I replaced mine with the Mojo Sight I had a bit of a time getting the new sight pressed in to the base and align the pinhole. I used a small pointed scriber that I ran through the hole in the base and upper ladder (a small drill bit would also do the job till you can get the pin started).
Now, concerning which rifle to buy: Right now , the Russian/Finn Mosin-Nagants in 7.62x54mm are everywhere and ammo is available, not as cheap as the 7.62x39 SKS stuff. The 8mm Mausers are also quite proliferent and ammo is easily obtained. It is an excellent caliber/rifle for scope hunting. The Swiss straight-pull 7.5mm is another very-good choice, only here I would be a little concerned about finding ammunition......... at least cheap ammunition.
For me, my choice would be an 8m Mauser hands down!! Reloading materials are available and most likely will continue to be available for some time.
